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Scientists weigh ingredients in recipe of the Universe

24.05.2002


An international team of scientists from Cambridge, Manchester and Tenerife has released the first results of new high-precision observations of the relic radiation from the Big Bang, often called the cosmic microwave background or CMB.



These observations have been made with a novel radio telescope called the Very Small Array (VSA) situated on Mount Teide in Tenerife. The images show the beginnings of the formation of structure in the early Universe.

From the properties of the image, scientists can obtain vital information on just what happened in the early universe and distinguish between competing cosmological theories.


Intriguingly, when combined with existing information on the CMB, they seem to show just how much the growth of the Universe itself (and of structures in it) is controlled by matter and how much by the mysterious dark energy that is now thought to pervade the vacuum of space.

The VSA telescope works by being able to detect very faint variations in the temperature of relic radiation – the radiation left over from the Big Bang.

Today we can see this radiation in all directions on the sky at a temperature of just three degrees centigrade above absolute zero, giving a picture of the Universe when it was just one 50,000th of its present age.

Because galaxies must have formed out of the primeval fireball, astrophysicists have predicted that they will have left imprints in the radiation. Across the sky, there should be tiny variations in the temperature of the relic radiation. However these are very weak - only one 10,000th of a degree centigrade.

During its first year of operation the VSA has observed three patches of sky, each some 8 x 8 degrees across. It can see detail down to one third of a degree, well matched to the typical size of interesting temperature variations.
The VSA has 14 aerials, each similar to a satellite TV dish but only 15 cm across. The signals from each aerial are combined, forming an interferometric array - a technique pioneered by Cambridge physicists.

The array is able to filter out unwanted terrestrial and atmospheric radiation allowing the the extremely faint CMB sky signal common to all the aerials to be detected. This approach allows high precision observations to be made at modest cost - the capital cost of the VSA was £2.6 million.

The performance of the VSA also results from using advanced receivers built at Manchester University and from the outstanding atmospheric conditions at the 2.4 km high Teide Observatory on Tenerife. The VSA can therefore measure specific, individual structures in the relic radiation with great precision.

A small number of other experiments have made similar observations. The different experiments work in different ways and face different challenges and sources of error; a key advantage of this diversity is that if their results agree, one can be confident that they are correct.

One special strength of the VSA is that it is an interferometer array; another is that it is able to robustly remove the contaminating radiation from radiogalaxies and quasars that lie between us and the CMB relic radiation.

The VSA results provide amazing confirmation of the current picture of the Universe.

Beck Lockwood | alphagalileo

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